The 50-metre short-course world record-holder won silver during the recent World Championships in Barcelona, which produced a record medal haul for Britain.
But Mr Foster said: "There is no future for British swimming unless we get children swimming."
He warned that it is not just competition that will suffer. "I hear about pool closures all the time. My father could not swim but he was determined that I would learn. People spend their holidays by the sea. How can parents relax if their children cannot swim?"